Let  fx=x+2x+1+2x-1. If fx=k  has exactly one real solution, then the value of k is not equal to

Let fx=x+2x+1+2x-1          =x-2x+1-2x-1,            x<-1x+2x+1-2x-1,            -1≤x≤1x+2x+1+2x-1,            x>1          =-3x,      x<-1x+4,     -1≤x≤15x,           x>1Graph of y=fx is as shown.Clearly, y=k can intersect  y=fxat exactly one point only if k=3